Diversity is used in communication systems such as wireless communication systems in order to enhance communication quality by transmitting information to be transmitted via various (space and/or time varying) channels. Diversity arrangements can be categorized as open-loop diversity and closed-loop diversity concepts. Closed loop diversity concepts apply a feedback of information from the receiver having received a diversity transmission to the transmitter to thereby perform a feedback control of the diversity transmission.
The closed-loop techniques adopted in 3GPP (3rd Generation Partnership Project) typically attempt to approximate the beamforming with perfect or average (spatial) channel state information in the transmitter. Then, one obtains array gains as the signal transmitted by the different antenna elements (forming an array) can be combined coherently. Naturally, conveying the channel state information with sufficient reliability and transmission rate can require a signaling channel of relative high capacity from the user equipment (UE) to the network and/or to the base station(s).
Note that the user equipment UE according to 3GPP and/or UMTS (Universal Mobile Telecommunication Standard) corresponds to a mobile station according to GSM (Global Standard of Mobile Communication). The present invention as described herein below is, however, not limited to be applied to a specific communication standard. References to UMTS 3GPP standard currently being developed serve as a mere example only and are not limiting the scope of the invention.
FIG. 1 shows in rough outline the feedback control arrangement for closed-loop diversity concepts. A communication network NW (e.g. UMTS or GSM or any other network) is represented by one of a plurality of Node_B (UMTS) (corresponding to a base station BS in GSM). The Node_B is provided with an array of antennas (not shown) from which a corresponding plurality of beams emerges in direction of the user equipment UE. Each beam in downlink direction travels and/or propagates via a transmission channel that can be represented by its channel transfer function h. The array of antennas thus leads to a matrix of channel transfer functions H representing the transmission behavior of the Node_B. For the purpose of the present invention, a Node_B and/or base station represents a first transceiver, while a user equipment UE and/or mobile station represents a second transceiver. However, the invention is not restricted to this but can be applied for any similar multi-antenna transmitter-receiver concept.
Upon receiving a plurality of at least two beams from the first transceiver via the plurality of transmission channels at the second transceiver, the second transceiver performs a well known processing to e.g. obtain the channel transfer functions (estimates), and derives control information for being fed back from said second transceiver UE to said first transceiver Node_B in order to accomplish a feedback control. Note that the channel transfer function estimates may, for example, be obtained using Viterbi detection and/or processing of pilot signals containing known training sequences, or by any other suitable known method.
W. Utschnik et al presented in the Proc. 4th European Personal Mobile Communications Conference, Vienna, Austria, February 2000, a contribution entitled “Efficient tracking and feedback of DL-Eigenbeams in WCDMA” by means of which a distributed implementation of the eigenspace/-beam tracking at the user equipment and the base station, respectively, was proposed with a corresponding feedback signaling. Since the adopted feedback signaling is fixed, it inevitably involves some overhead being transmitted back and at least occupies feedback signaling capacity which could be used otherwise more efficiently.
In the 3GPP TSG RAN WG 1 Meeting #14, Jul. 4-7, 200, Oulu, Finland, Siemens submitted a proposal for an “Advanced closed loop Tx diversity concept (eigenbeamformer)” for discussion. The required feedback signaling used in the thus proposed arrangement is still considerable and thus also at least occupies feedback signaling capacity which could be used otherwise more efficiently.